Process and material for the direct production of positives by the silver salt diffusion process



United States Patent PRGCESS MATERIAL FOR THE DIRECT PRO- DUCTION 0F PGSITIVEES BY THE SILVER SALT DEFUSION PRQCESS Edith Weyde, Leverkusen-Burrig, Germany, assignor to Agfa Aktiengesellschaft, a corporation of Germany No Drawing. Filed May 27, 1957, Ser. No. 661,606

Claims priority, application Germany June 9, 1956 9 Claims. (Cl. 91629) This invention comprises an improved process for the direct production of positive photographic images and new photographic materials for use in the process.

In French Patent 879,995 there is described a photographic process for the direct production of positive images, hereinafter referred to as silver salt diffusion process, according to which a light sensitive silver halide emulsion layer, hereinafter referred to as negative layer, after being exposed to an object is developed in the presence of a silver halide emulsion layer being in close contact during said developing process with a light non-sensitive reception layer, hereinafter referred to as transfer layer, containing nuclei for development, or substances producing such nuclei for development. During this process the exposed part of the silver halide emulsion layer is developed to a negative image of the object to which it had been exposed while at the same time part of the non-exposed silver halide is dissolved by the silver halide solvent. This dissolved silver halide diffuses to a transfer layer, Where it is reduced to a positive image by the developer under the catalytic action of the nuclei for development present in said layer. The meaning of the terms negative and positive as used in this description is relative, which means that if the emulsion layer is exposed to a negative, a direct negative will be produced in the transfer layer whereas if the emulsion layer is exposed to a positive a direct positive will be obtained in said transfer layer.

The ease with which the separation of the two layers is effected depends substantially on thechoice of the coating agents for the negative and positive layers, as described in British patent specification 687,751. For example, if gelatine is used for both layers, the two layers adhere very strongly to one another and they must be quickly separated from one another, while the addition of for example a cellulose ester to one of the layers enables these layers to be separated from one another more easily, even after a much longer time. However, all these layers can only be separated from one another if they are still moist. For example, if the layers are completely dried while still in contact, it is impossible to pull them apart.

It has now been found that the separation of the two layers can also be carried out after complete or almost complete drying if the binding agent of at least one of the layers comprises starch ethers and/or galacto-mannans. Suitable starch ethers are derivatives of starch in which one or more hydroxyl groups per anhydroglucose unit are etherified with organic compounds for example with methyl alcohol, ethyl alcohol, propylalcohol,butylalcohol, =allylalcohol, laurylalcohol, benzylalcohoL' Further suitable starch ethers are the hydroxyalkylethers and the carboxyalkyl ethers, such as those in which the anhydroglucose units contain at least one of the groups: -OCH .COOH, O-CH .CH .OH,

' O -CH .CH ,.CH .OH, --O.CH CH NH O.CH .CH C-N. Suitable galactomannans are for instance Guar Gum, Locust Bean Gum (compare Natural Plant Hydrocolloids, Advances in Chemistry, Series 11, pages 45-50, published by American Chemical Society). It is preferred to use the aforementioned substances as binding agents for the transfer layer, because it is possible in this case to dispense completely with the addition of gelatine or other binding agents, this not being so readily possible in the preparation of the negative emulsions. Coating solutions are prepared from the starch derivatives and the galactomannans by dissolving them in water or organic solvents, such as acetone, or mixtures of water and organic solvents. The concentration of the starch derivative solution is preferably about l-S percent, whereas that of the galactomannan is preferably about 1-2 percent, although other concentrations may be used.

It is readily possible to add the substances necessary for the silver salt diffusion process to the solutions of the starch derivatives and/or gal-actomannans, examples of such substances being development nuclei including noble metals, such as colloidal silver or gold, and colloidal sulfides and selenides of heavy metals such as silver, gold, lead, mercury, tin, copper. These development nuclei may be added to the coating solution in the form of colloidal solutions, or they may be produced in the coating solution, or in the coated layers according to known methods. The said nuclei are preferably applied in amounts of 0001-1 g. per litre of coating solution. To the coating solutions there may furthermore be added silver halide solvents such as sodiumthiosulphate, and calciumthiosulphate.

If a paper coated in this manner is used as a transfer material, it is possible to use gelatine as a binding agent for the negative layer. For processing, the two layers are brought into contact in the usual manner and they can then be separated from one another at any desired time. The two layers can however be dried by heat while still in contact, for example by passing them over a heated roll, in order thereafter to strip them from one another. It is very advantageous in such a case to dry the layers in such a way that the negative layer remains moist for a somewhat longer period than the positive layer. This can be achieved by passing the two layers while in contact with each other through a pair of nipping rollers, of which only that one is heated which is contacted with the positive material, the temperature of the heated rolls being about IOU-150 C. The result which is obtained is that the salts, which quite generally tend to migrate to those areas of such a system which remain moist for the longest period, are concentrated in the negative layer, while their concentration in the positive layer is correspondingly lower. This question is important if the transfer material is to remain white during relatively long storage.

The coating solutions can, if desired, have added thereto a small proportion of gelatine or another binding agent, but preferably only in an amount not surpassing 20% of the total weight'of the binding agents. Such further binding agents are, for instance, gelatine, polyvinylalcohol, cellulose ether, such as methylcellulose, hydroxyethyl-cellulose, cellulose esters, such as partially esterified cellulose acetate, cellulose phthalate, polyvinylpyrrolidone, aqueous dispersions of polyacrylonitrile, polyvinylchloride or further water-insoluble polymers of copolymers.

The separation of the layers can also be assisted if a matting agent, such as for example starch, ethyl-cellulose, barium sulphate and titanium dioxide, is added to the negative layer (about 10-100 g. of matting agent per 1 litre of silver halide emulsion), or if part of the gelatine of the emulsion layer is replaced by another binding agent, such as for example one or several of the aforementioned starch ethers or galactomannans, or a cellulose ether, such as methylcellulose, these binding agents being preferably applied in amounts of 1-20percent as calculated on the weight of gelatine.

instance Example 1).

7 i 3 EXAMPLE 1 Preparation of the Negative Layer As negative layer, there is used a silver chloride emulsion with gelatine as binding agent, the emulsion being prepared according to known specifications.

Preparation of the Transfer Layer A 2% aqueous solution of starch methyl ether, to one litre of which the following substances are added:

0.01 g. of silver sulphide in colloidal form,

30 g. of sodium thiosulphate and the Wetting agent necessary for the casting, such as for example saponin,

is cast in known manner on a support, for example paper, to form a layer, and dried.

The processing is carried out in the manner usually employed for the silver salt diifusion process. As a de' veloper there may be used the following solution:

2.5 g. p-methylaminophenolsulphate g. hydroquinone 2 g. KBr

g. Na SQ 30 g. NaOH The two sheets are however not separated after being passed through the developer, but are passed over a hot 'roll and are only stripped from one another after being completely dried.

EXAMPLE 2 Preparation of the Negative Layer 100 cc. of a 5% solution of the sodium salt of cat-boxymethyl cellulose are added per litre of a silver chloride emulsion which has-been prepared according to conventional specifications.

Preparation of the Transfer Layer Preparation of the Negative Layer 7 50 g. of starch suspended in water are added per litre of a silver chloride emulsion which has been prepared in the usual manner, and the emulsion is cast in the usual way to form a layer.- 7

Preparation of the Transfer Layer A 2% solution of starch hydroxyethyl ether is used, 100 cc. of a 3% gelatine solution being added per litre of the starch ether solution. The other additives correspond to those of Example 1. The solution is cast to form a layeron a paper support.

The processing takes place in the usual way (see for After the two sheets in contact with one another have left the developer, they are passed between'a pair of rolls, one of which is heated. Care is taken that the positive paper faces the hot roll. After passing through the rolls the papers are practically dry and can easily be separated from one another.

EXAMPLE 4 Preparation of the Transfer Layer vA 1% aqueous solution of guar gum, to one litre of which 0. 01 g. of colloidal silver sulphide, g. of sodium thiosulphate and a Wetting agent are added, is cast in known manner on a paper support, and dried.

This transfer layer may be used for the production of positive silver images in combination with the negative layers in the manner disclosed in the preceding examples.

What I claimed is:

1. A layer material suitable as transfer material for the silver salt diffusion process comprising a support and a colloid layer coated on said support, the binding agent of said colloid layer being essentially a compound of the group consisting of starch ethers and galactomannans, said starch ethers being starch that has been etherified with a radical of the class consisting of aliphatic, araliphatic, hydroxyalkyl, carboxyalkyl, aminoalkyl and cyanoalkyl groups, and said colloid layer containing dispersed silver halide development nuclei that cause development of unexposed silver halide.

2. A layer material according to claim 1, wherein the binding agent also includes a different binding material in an amount not surpassing 20 percent of the total Weight of binding agent.

3. A layer material according to claim 2, wherein the dilferent binding material is gelatine.

4. A layer material according to claim 1, the colloid layer of Which contains a silver halide solvent.

5. In the process for the production of direct positive silver images by developing a photographically exposed silver halide emulsion layer in the presence of a silver halide solvent while said silver halide emulsion layer is in direct contact with a transfer layer in the form of a binding agent holding nuclei that cause unexposed silver compounds to be reduced to silver by developing agents, whereby at the unexposed areas of the silver halide emulsion layer soluble silver complexes are formed and are transferred to the transfer layer Where they are reduced to positive silver images, and thereafter separating the two layers from each other, the improvement according to which the binding agent is a member of the group consisting of starch ethers and galactomannans, said starch ethers being starch that has been etherified with a radical of the class consisting of aliphatic, araliphatic, hydroxyalkyl, carboxyalkyl, aminoalkyl and cyanoalkyl groups, and the transfer layer is dried before being separated from the emulsion layer.

6. The process. as defined in claim 5 wherein the silver halide emulsion layer has its silver halide held in a binding agent of gelatin containing from 1 to 20% by weight of a member of the group consisting of starch ethers and galactomannans, said starch ethers being starch that has been etherified with a radical of the class consisting of aliphatic, araliphatic, hydroxyalkyl, carboxyalkyl, aminoalkyl and cyanoalkyl groups.

7. The process as defined in claim 5 in which the transfer layer is dried by passing the contacted layers between and in engagement with a heated pair. of solid surfaces.

8. The process as defined in claim 7 in which only one of the solid surfaces is directly heated, and the contacted layers are passed between the surfaces with the transfer layer against the directly heated surface, and the directly heated roller being at a temperature of about to C.

9. The process as defined in claim 5 in which the emulsion layer also contains about 10 to 100 grams of matting agent per liter of emulsion.

References Cited in the fileof this patent UNITED STATES PATENTS (Qther references on foliowing page) 6 UNITED STATES PATENTS OTHER REFERENCES 2,971,840 Haydn et a1. Feb. 14, 1961 CE. Dig. of Fed. of Paint and Varnish Production FOREIGN PATENTS llxlirch 1945, pages 111, 117, copy 1n D1v. 56

687,751 Great Britain Feb. 18, 1953 5 Outlines of Biochemistry, Gortner, May 1953, page 654, 748,892 Great Britain May 16, 1956 copy in Div. 60. 

5. IN THE PROCESS FOR THE PRODUCTION OF DIRECT POSITIVE SILVER IMAGES BY DEVELOPING A PHOTOGRAPHICALLY EXPOSED SILVER HALIDE EMULSION LAYER IN THE PRESENCE OF A SILVER HALIDE SOLVENT WHILE SAID SILVER HALIDE EMULSION LAYER IS IN DIRECT CONTACT WITH A TRANSFER LAYER IN THE FORM OF A BINDING AGENT HOLDING NUCLEI THAT CAUSE UNEXPOSED SILVER COMPOUNDS TO BE REDUCED TO SILVER BY DEVELOPING AGENTS, WHEREBY AT THE UNEXPOSED AREAS OF THE SILVER HALIDE EMULSION LAYER SOLUBLE SILVER COMPLEXES ARE FORMED AND ARE TRANSFERED TO THE TRANSFER LAYER WHERE THEY ARE REDUCED TO POSITIVE SILVER IMAGES AND THEREAFTER SEPARATING THE TWO LAYERS FROM EACH OTHER THE IMPROVEMENT ACCORDING TO WHICH THE BINDING AGENT IS A MEMBER OF THE GROUP CONSISTING OF STARCH THAT HAS BEEN ETHERIFIED WITH A RADICAL ETHERS BEING STARCH THAT HAS BEEN ETHERIFIED WITH A RADICAL OF THE CLASS CONSISTING OF ALIPHATIC ARALIPHATIC, HYDROXYALKYL, CARBOXYALKYL AMINOALKYL AND CYANOALKYL GROUPS, AND THE TRANSFER LAYER IS DRIED BEFORE BEING SEPARATED FROM THE EMULSION LAYER. 